This invention relates to lightwave communication systems and, more particularly, to circuits for selectively operating redundant light sources in fiber optics systems.
In certain lightwave system applications, especially those where maintenance is difficult, selectively operated redundant light sources are a useful expedient. In particular, if the operating source fails, the system as a whole need not fail because circuitry is provided which is responsive to the failure mode of the source to automatically bring into operation a redundant source.
One application fitting this prescription is a lightwave submarine cable system in which a fiber optic cable connecting transoceanic terminals is laid on the ocean floor. The cable includes a plurality of repeaters spaced along its length for amplifying the lightwaves. In one contemplated system, the lightwaves are detected in each repeater by a photodiode. The corresponding electrical signals are amplified, and the lightwaves are then regenerated via a light source. Without redundancy the failure of the repeater light source would interrupt transmission and hence customer service. The interruption could extend for long periods of time because, obviously, repairing the repeater might entail raising the cable from the ocean floor to a repair ship on the ocean surface. On the other hand, the use of redundant sources in the repeaters would reduce the likelihood that such expensive and time-consuming repairs would be encountered.